This invention relates to an improved protected membrane roofing system or the like for a residential or commercial building, deck structure and similar structures. More particularly, this invention relates to an insulation panel for a protected membrane roofing system for insulating the interior of a building from ambient thermal cycling and for insuring water impermeable integrity of the roofing membrane.
The basic concept of a roof is to act in cooperation with wall surfaces to form an enclosed space which may be isolated from an ambient environment and thus may be temperature and humidity regulated in accordance with intended utilization.
A threshold or common denominator of almost all controlled environments is to maintain the enclosure in essentially a water tight or dry condition. Accordingly over the years the roofing industry has attempted to maintain a water tight or water impermeable roof condition by building a water impermeable barrier, in situ, upon a roof substructure or deck. Such a water barrier has typically assumed the configuration of a laminar composite comprising a plurality of bituminous felt layers with intercalated courses of mopped on bituminous composition.
In many previously known installations, bituminous compound arrives at a job site in solid cylinders. The cylinders are melted in a heater and the hot liquid is then carried in buckets to a roof deck where it is mopped onto a previously prepared roof substructure. A roll of bituminous impregnated felt paper is then carried to the roof and unrolled upon the hot bituminous compound which binds the felt to the roof deck. Three or more courses are then built up over the entire roof structure. The job is finished with a layer of topping gravel. The gravel weights down the felt courses and also serves as a shield to minimize ultra-violet degradation of the felt and bituminous membrance.
Although water impermeable roofing membranes, as previously noted, have been widely utilized in the roofing industry substantial disadvantages have been occasioned. In this connection, elevated roof temperatures may vaporize volatile components in the bituminous compound. The compound then tends to harden and crack in a checkered or "allegator" array. Moreoever as the bituminous compound becomes hot during the summer months the overlay course of gravel tends to sink into the membrane. Further, prior roofing systems often developed vapor blisters, splitting or ridging.
The above factors each tended to create water seepage difficulties which ultimately rendered the waterproofing system unsuitable for its intended purpose.
In addition to water impermeability considerations environmental control criteria dictates internal isolation from thermal cycling which takes place at the exterior surface of a roof. More particulalry the exterior surface of a roof may experience temperatures during midsummer as high as 180.degree. Fahrenheit while a winter cold front may drop the temperature to as low as 20.degree. or 30.degree. below zero. The interior surface of the roof, however, should optimally be maintained at a desired interior temperature which typically is 65.degree. to 75.degree. Fahrenheit.
In order to provide thermal protection, an initial practice entailed lining the interior surface of the roof with an insulation composition such as sprayed or layered glass fibers, fiberboard, plastic foams and the like. While such insulation techniques operably reduced thermal cycling problems it severely accentuated the previously outlined difficulties occurring with the felt and bituminous water barrier by isolating the barrier from a relatively stable interior temperature of the building structure. Accordingly, in the past it was not uncommon for roof membranes to require considerable attention and periodic replacement.
One advance was made in the roofing art when it was determined that an insulation course could be installed exteriorly on top of the felt and bituminous water barrier. The exterior insulation provided a building with isolation from thermal gradients and concomitantly physically protected the felt and bituminous waterproofing barrier.
In the above connection, an insulated roof membrance assembly which has attained at least a degree of industry recognition comprises a water barrier of felt and bituminous lamination which is built up, in situ, in a manner as previously discussed. A hot course of bituminous compound is then mopped upon the final layer of felt and generally rectangular panels of polystyrene are laid directly upon the hot bituminous compound. The polystyrene insulating members are abutted against each other and a heavy course of aggregate is applied directly upon the upper surface of the thermal insulating members to hold the members in place and isolate the insulation surface from ultra-violet degradation.
While such a system, as previously noted, has achieved at least a degree of industry recognition and utilization, room for significant improvement remains.
In this regard, an insulated roof membrane assembly as described in the proceeding permits rain water to seep downwardly around lines of panel abutment. The water then migrates beneath the panel and tends to lift or float the panels. In order to obviate this tendency of the insulation to float a substantial amount of gravel needs to be applied directly to the insulation course in order to maintain it in place. In this connection, gravel may be deposited at a rate of 1,000 pounds or more per 100 square feet. The roof deck must therefore be designed to support a considerable amount of weight.
Additionally, rain water which collects in the insulation fissures and beneath the insulation panels strikingly reduces the insulation effectiveness and can even, over time, permeate and degrade the insulation.
The problems suggested in the proceeding are not intended to be exhaustive, but rather are among many which may tend to reduce the effectiveness of prior insulated roofing membrane assemblies. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that insulated, water impermeable roofing systems appearing in the past will admit to worthwhile improvement.